1. Field of the Invention
This invention relates to the use of surfactant salts to enhance the recovery of oil from oil-bearing formations. In particular, the invention relates to the use of surfactant salts which have stability in brines and stability in the presence of polymers used as mobility improvers.
Waterflooding is a well-known technique for the secondary or tertiary recovery of oil from subterranean formations from which oil has previously been recovered by primary techniques such as pumping, natural flow and the like. In many areas the only economic source of water is a brine and the brine usually contains various metal ions such as calcium, magnesium and the like. As used herein brine means a sodium chloride brine.
The use of surfactants to reduce the interfacial tension between the water and the oil to be displaced from the formation is also well known and the literature is replete with different surfactants and combinations thereof useful in waterflooding processes. It is well known that the effectiveness of any given surfactant material varies considerably with such factors as temperature of the water, the amount of salt in the water, the amount and type of metal ions in the water and the like.
The invention relates to the recovery of oil from subterranean oil reservoirs and also to improved waterflooding operations involving the injection into a high temperature reservoir of an aqueous liquid formulated through the use of an ether sulfonate surfactant.